Larvae:All of the Brachyentridae family caddisflies are tube case makers that build cases that look like tiny chimneys. Not all of them are square. Some are rounded.These all were found in the Smokies. Although the cases are usually attached to rocks or wood, they are still eaten by trout. The larvae attach their cases with silk anchor lines that they produce. These drift with the current a few inches away from their point of anchor while they gather food.Others say that imitations of this larvae in its case can be effective at times. I cannot confirm that for the Grannoms because I have not tried it. I have caught trout on other caddisfly larva imitations and I would expect the chimney case imitations would also work.I do know that the water is cold, from 45 to 55 degrees, during the time period these early season hatches are taking place. In fact, some days after the hatch has started and the weather turns especially cold you can find the adults on the banks usually on rocks or wood of some type - sticks, logs, etc., in a dormant state. You can just pick them up. They will try to crawl but cannot fly. Later in the day when the weather warms, they will start to fly and continue the mating and egg laying process. I mention this in the larva section because it is during these mornings that the larvae would probably be most effective. If you are on the stream fishing prior to the start of the hatch, which usually is the middle of the afternoon or the warmest part of the day, then fishing imitations of the larvae may work. These larvae are very active. They will amaze you as to how well they can crawl, still inside the chimney cases. I have captured this on video several times.